Encapsulation of Zanthoxylum bungeanum essential oil in a tea saponin-stabilized nanoemulsion for enhanced insecticidal control of Cryptolestes ferrugineus

To overcome the inherent limitations of Zanthoxylum bungeanum essential oil (ZBEO), such as high volatility and poor water solubility, a potentially green nanoemulsion was developed using tea saponin (TS) as a natural co-stabilizer with Tween 80 for the enhanced insecticidal control of Cryptolestes ferrugineus . The optimized formulation (ZBEO: Tween 80:TS = 2:1:1, w/w) exhibited a small droplet size (165.49 ± 2.98 nm), low polydispersity index (0.29 ± 0.02), and high negative zeta potential (−34.79 ± 3.02 mV). This stability originated from a synergistic mechanism between Tween 80 and TS: Tween 80 provided steric hindrance, while TS contributed electrostatic repulsion at the oil-water interface. Bioassays demonstrated that nanoencapsulation significantly enhanced the insecticidal efficacy of ZBEO, reducing the LD 50 for contact toxicity and the LC 50 for fumigation toxicity by 25 % and 41 %, respectively. Notably, after 90 days of storage, the nanoemulsion retained substantial bioactivity, with only a minifmal increase in LC 50 values, and remained significantly more effective than freshly prepared, unformulated ZBEO. The enhanced performance could be attributed to improved cuticular penetration and controlled release enabled by the TS-based stabilization system. This work confirms TS as an efficient natural co-stabilizer and presents the ZBEO nanoemulsion as a promising, high-efficacy candidate based on natural components for stored-grain pest management.